The various methods of forming an image by exposing a photographic light-sensitive material include an image-forming method which employs a so-called scanner system. In a scanner system, an original is scanned and a silver halide photographic material is exposed based on the image signals obtained by scanning to form on the photographic light-sensitive material a negative or positive image corresponding to the image of the original.
There are various kinds of recording apparatus which have been used in practice in image-forming methods that employ scanner systems. As the recording light source for the recording apparatus used in scanner systems, glow lamps, xenon lamps, mercury lamps, tungsten lamps, light emitting diodes, etc., have been used.
These light sources, however have recognized disadvantages for practical use. Typically, their output is weak and their average life is relatively short.
To overcome these disadvantages, scanner systems have been developed that use a coherent laser light source such as an Ne--He laser, an argon laser, an He--Cd laser, etc. By using coherent light sources of this type, a high output is obtained. However, scanner systems using such light sources suffer from disadvantages in that the apparatus is typically large and expensive and a modulator is required. Further, since a visible light is used and the photographic material is necessarily of the type that is sensitive to visible light, the types of safelights that can be used are restricted, so that handling of the light-sensitive materials becomes problematic.
Scanner systems that employ semiconductor lasers have also been developed. Semiconductor lasers have the advantages that the device for the laser is small and inexpensive, the laser light can be easily modulated, and the life of the semiconductor laser is longer than those of the foregoing conventional lasers. Also, a light-sensitive material having a sensitivity in the infrared region can be used since the laser emits light in the infrared wavelength region. This allows a bright safelight to be used and handling of the light-sensitive material is simplified.
However, since the output of the semiconductor lasers which are presently available is not always high, the sensitivity of conventional light-sensitive materials for use in scanner systems employing semiconductor lasers is inadequate to carry out a scanning exposure of a large picture size in a short period of time. Accordingly, a light-sensitive material having an improved sensitivity in the infrared region has been demanded.
Known methods of increasing the sensitivity of photographic light-sensitive materials include increasing the grain size of the silver halide grains and adding various chemical sensitizers to the silver halide emulsion. These methods, however, are frequently accompanied by an increase in the graininess of the silver images and the formation of fog, and hence they are unsuitable for light-sensitive materials for use in scanner systems requiring a sharp image quality.
U.S. Pat. No. 4,975,362 discloses sensitizing dyes which are asserted to be effective for improving infrared sensitivity but these sensitizing dyes do not always provide a sufficiently high sensitivity to light sources of various wavelengths.